Optical absorption measurements require a laboratory calibration value for determining physical variables such as extinction and the consequent transmission, absorption, etc. This laboratory calibration value is generally determined in a liquid calibration solution preferably, demineralized or ultrapure water.
Adjusting the laboratory calibration value to compensate for any system changes in the sensor over its lifespan is essential for achieving correct measurements. For this, a liquid calibration solution must be provided.
The quality of the laboratory calibration strongly depends upon the quality of the calibration solution. It cannot always be guaranteed that superior quality demineralized or ultrapure water is available on-site. These therefore need to be brought by the customer or service employee. Entrained materials from contaminated containers are possible. Moreover, to achieve satisfactory results, the measuring system and calibration solution must be in a thermodynamic equilibrium. Depending upon the application and differences in temperature between the two systems, this can take several minutes.